The present invention relates to an improved vibratory gyroscope which senses a Coriolis Force for the purpose of detecting angular velocity.
FIG. 13 illustrates an example of a conventional vibratory gyroscope in an XYZ coordinate system.
This kind of gyroscope provides a metal tuning fork 7 fixed on a base plate 9 through a support member 8, and a pickup member 10 extending from the base member 6 in the direction of the X-axis. The tuning fork is monolithically or integrally formed from a base member 6 and two arm members 4 and 5, with the two arm members 4 and 5 extending in parallel in the direction of the Z-axis and being separated by a certain distance in the direction of the Y-axis and abutting the base member 6 at each lower end.
In the above vibratory gyroscope, it is known that a Coriolis Force F.sub.c is exerted on each arm member 4 and 5 which acts in mutually opposite directions along the X-axis, when the arm members 4 and 5 are symmetrically vibrated with speed V in the direction of the Y-axis by means of piezoelectric or magnetic elements, e.g., by applying alternating currents to piezoelectric ceramics 11 and 12, at the same time that the tuning fork 7 is caused to rotate about the Z-axis with the angular velocity .omega..
Since the speed V of the arm members 4 and 5 changes alternately, the generated Coriolis Force is modulated by the vibrations of the arm members 4 and 5. The tuning fork 7 torsionally vibrates about the Z-axis with respect to the base plate 9, the torsion angle being proportional to the velocity .omega..
This conventional device detacts the magnitude of torsional vibration through piezoelectric or magnetic elements, using the pickup member 10 extending in the direction of the X-axis. For example, in case of detection by piezoelectric elements, the torsional vibration of the tuning fork 7 is developed as a flexural vibration in the pickup member 10, and bimorph elements on the pickup member 10 produce electric charges according to the magnitude of the flexure, which electric charges are measured as electric voltage.
However, in such a prior art system, there is a possibility that vibration of the arm members 4 and 5 produces undesired vibration of the base member 6 in the direction of the Y-axis due to an imbalance in the weight and length of the two arm members 4 and 5, thereby causing the pickup member 10 to generate undesired detection signals including offsets, which offsets appear as if a Coriolis Force is detected in spite of the fact that the angular velocity is zero, and also lower the signal to noise ratio of the detection signals and the detection sensitivity of the gyroscope system as a whole.
In accordance with a conventional method for reducing such offsets, measurement of the offset signal level is carried out before operation of the gyroscope system, and the detacted signal level during the operation of the gyroscope system is then subject to correction based upon the measured offset signal level. More specifically, before application of angular velocity to the gyroscope system, the output signals of the pickup member 10 are detected by a synchronous detector and then rectified to direct currents by a rectifier. Since the level of such direct currents represents the offset level, the baseline level of the detection signals is changed based upon the level of such direct currents so that the offsets may be cancelled. However, it has been substantially unavoidable for such prior methods to reduce the offsets sufficiently and effectively because the sensitivity of the pickup member 10 fluctuates slightly depending upon the temperature of the location where the gyroscope is placed.
Additionally, according to the prior art, providing a pickup member which extends in the direction of the X-axis has inherent drawbacks due to its complexity of construction, large size, and cost to produce.
Accordingly, a principal object of the present invention is to provide a new vibratory gyroscope with improved performance in detection sensitivity.
A further object of the present invention is to provide a new vibratory gyroscope with reduced size and simplified construction.
A further object of the present invention is to provide a new vibratory gyroscope with reduced offsets in its output signal.
A further object of the present invention is to provide a new vibratory gyroscope with improved signal to noise ratio in its output signal.
A further object of the present invention is to provide a new vibratory gyroscope with improved manufacturing efficiency.
A further object of the present invention is to provide a new vibratory gyroscope with improved manufacturing processing.
A further object of the present invention is to provide a new vibratory gyroscope with reduced manufacturing costs.
A further object of the present invention is to provide a new vibratory gyroscope with greater tolerance in the size and weight of the arm members of a tuning fork.